Can Dogs and Cats be Allergic to Penicillin?

February 26, 2015

By Linda Cole

In 1928, a Scottish bacteriologist named Alexander Fleming discovered penicillin while tidying up his lab. He was about to toss a moldy petri dish into the trash when he noticed something strange about the bacteria – it wasn’t growing as well as it should have been. However, it would be another twelve years before penicillin would become a lifesaving drug; two Oxford scientists – Howard Florey and Ernst Chain – produced a brown powder capable of retaining the antibacterial properties in 1940.

The new drug was rushed into mass production and sent to the war front during the early years of WWII. Today, penicillin is used to treat anything from minor wounds to tonsillitis and pneumonia. Unfortunately, some people are allergic to penicillin. Is it possible for dogs and cats to have an allergic reaction too?

Penicillin works by inhibiting bacteria from building a sustainable cell wall. Fleming noticed that mold on the petri dish was attacking bacteria surrounding it to get more space and nutrients it needed to grow, by releasing a bacteria killing compound that prevented some bacteria from forming new cell walls. This process is called antibiosis, which is where the word antibiotic comes from. Once Fleming isolated and identified the antibacterial compound, he named it penicillin. The discovery of penicillin was hailed as the first miracle drug, and has saved countless number of human and animal lives over the years.

A penicillin allergy may be caused by environmental factors, something that’s inherited, or it could be both. An allergic reaction can be mild, severe or life-threatening, and symptoms may not appear until an hour or longer after taking penicillin.

Amoxicillin is a derivative of penicillin, and both antibiotics are used by vets. However, amoxicillin is more widely administered because it’s tolerated better by the body, works on more kinds of bacteria, and is easily absorbed by the body. This antibiotic is used to treat wounds and other injuries, tooth abscesses, skin infections, ear infections, urinary or bladder infections and respiratory infections.

Dogs and cats can have an allergic reaction to penicillin, including amoxicillin. Symptoms to watch for include difficulty breathing, rapid heartbeat, rash, hives, seizures, heavy drooling, vomiting, fainting, unusual bruising or bleeding, and swelling of the lips, face or tongue.

Years ago my cat, Buddy, developed an ear infection and my vet prescribed amoxicillin. I gave Buddy his first dose and he reacted to it within an hour. Since he wasn’t feeling well I was keeping a close eye on him, but it never occurred to me it was possible for a cat to have an allergic reaction to penicillin or amoxicillin. Buddy was very agitated and breathing heavily. I called my vet and was told to monitor him and bring him in if his condition worsened. He said it might be possible a cat could have an allergic reaction, but wasn’t sure at the time. To be on the safe side, I was instructed not to give Buddy any more of his medicine. I wrapped him up in a blanket and held him until he calmed down and his breathing returned to normal a few hours later. He was fine, but I had to use another medication for his infection.

If you think your pet is having an allergic reaction to penicillin, amoxicillin or any other medicine, take him immediately to your vet. A severe reaction can become life-threatening. When prescribed for a dog or cat, amoxicillin is normally given for a week. It’s important to give your pet all of the medication even if he seems better after a couple of days. Not finishing it can cause bacteria to become resistant and create problems in the future for your dog or cat.

Because bacteria dies at different times, amoxicillin needs to be administered correctly each day and for the length of time it’s prescribed for it to kill all of the bacteria. If you miss a dose, call your vet for instructions.

Penicillin can interfere with other kinds of medication. When your vet prescribes an antibiotic, make sure he is aware of any other medications your pet is on. If your dog or cat has had an allergic reaction to penicillin, it’s up to you to question future prescriptions to make sure they don’t contain penicillin or derivatives of the drug.

Any medication, including flea control, can cause an adverse reaction in pets. Never hesitate to call your vet if you think your pet is having a reaction.

Top photo by Aiko, Thomas & Juliette/Flickr
Bottom photo by Ilmicrofono Oggiono/Flickr

Read more articles by Linda Cole

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  1. Donny Cox says:

    I talked to my vet at Overland animal in Overland, Mo. and they told me my dog’s seizure’s were’nt cuz of amoxicillin. but he’s been taking it for almost 2 yrs now cuz of his teeth. (extended time taking Amocicillin) I could’nt get thru to this idiot.